The present invention relates to plasma vacuum pumps, and in particular relates to plasma pumps that use an Applied Plasma Duct System (APDS).
In many industrial processes employing plasmas, such as PECVD, etching, or other surface modifications of workpieces, for example, semiconductor devices such as VLSI chips, it is generally considered by those skilled in the art to be advantageous to generate the processing plasmas in suitable mixtures of gases maintained at pressures as low as 1-10 milliTorr. The purity and composition of the gas can best be controlled if the flow rate of fresh gas into the processing chamber is high relative to the processing rate. However, existing vacuum pumping technology can provide only limited throughput of gas in this pressure range. The pumping speed of widely used turbomolecular vacuum pumps, for example, generally decreases rapidly with increasing pressure at pressures above roughly 1 milliTorr. It would greatly facilitate the pumping of process gasses if a robust, cost-effective technology capable of high-speed pumping in the pressure range from 1-10 milliTorr were readily available.
For some time there has been a growing appreciation of the possible benefits of using the plasmas themselves as the active element in vacuum pumping technologies; for example, plasmas can pump a wide range of gasses, including hydrogen and helium, with equally high efficiencies; and plasma vacuum pumps can be highly tolerant of solid or corrosive process by-products.
These potential benefits have not yet been fully realized in practice for a number of technical reasons relating to efficient generation of plasma, the creation of a magnetic field suitable for both the plasma processing and the necessary channeling of the plasma flow, and simple and effective mechanisms for driving the plasma flow at pressures in the range of importance to plasma processing applications. In addition, the problem is exacerbated by the plasma""s ability to shield its interior from low-frequency external electric fields, together with the complex atomic and molecular processes that become important in the pressure range of interest.
A plasma vacuum pump was described by Dandl in xe2x80x9cMethod and Apparatus Using Electron Cyclotron Heated Plasma for Vacuum Pumpingxe2x80x9d, U.S. Pat. No. 4,641,060, issued on Feb. 3, 1987. This plasma vacuum pump provided high pumping speeds for all gases with no moving mechanical parts at gas pressures below 1 milliTorr.
The primary object of the present invention is to provide a plasma vacuum pump for plasma processing applications.
The above and other objects are achieved, according to the present invention, by a plasma processing system comprising: a plasma processing chamber; and plasma pump to pump particles from a first region in the plasma processing chamber containing a plasma to a second region containing a plasma at a higher pressure, wherein the plasma pump comprises a plurality of applied plasma duct system (APDS) cells, wherein each APDS cell comprises: a conduit having an inlet end, an outlet end, and a longitudinal axis extending from the inlet end to the outlet end, the conduit fluidly coupled to the first region and the second region; a magnetic field generator, constructed and arranged to generate a magnetic field having field lines generally parallel to the longitudinal axis; and an electric field generator, constructed and arranged to generate an electric field having field lines generally parallel to the longitudinal axis, such that charged particles within the conduit are accelerated longitudinally so as to pass through the conduit outlet.